Thanks Larry and Ghislain- This is what I expected, just wanted to double check that I wasn't missing something. --jono
On Thu, Aug 27, 2015 at 11:40 AM, Ghislain Vaillant <[email protected]> wrote: > On 27/08/15 19:23, Jonathan Gibbs wrote: > >> Has anyone played with OIIO's FFT functions? I've not worked with this >> much, but what I'm used to seeing out of the FFT is an image with a >> white pixel in the center and some matter of pixels around those. >> >> (For instance: http://homepages.inf.ed.ac.uk/rbf/HIPR2/fourier.htm) >> > > This is one convention of looking at the spectral content of an image, > i.e. [-N/2 -> N/2-1] with the DC component at the center... > > What I get out of OIIO is an image with interesting bits in the 4 >> corners and nothing in the middle. Am I right to interpret pixel (0,0) >> as the lowest frequency in X and Y and pixel (max,max) as the highest >> frequency in both X and Y? >> > > But OIIO uses the convention used by FFTW which is [0 -> N/2-1; -N/2 -> > 1]. You would need to do an FFT shift (swap quadrants wrt the center) to > get the data in a centered layout. > > MATLAB's or Numpy's fft / fftshift documentation gives you further > rationales behind the centered vs fftw layouts. > > Ghis > _______________________________________________ > Oiio-dev mailing list > [email protected] > http://lists.openimageio.org/listinfo.cgi/oiio-dev-openimageio.org >
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